Chair backrest



FIG. 1 is a front perspective view of the chair backrest of the present design as part of a theater style chair;

FIG. 2 is a side elevation view of the chair backrest of the present design, the opposite side view being a mirror image thereof;

FIG. 3 is a front perspective view of the chair backrest of the present design;

FIG. 4 is a back elevation view of the chair backrest of the present design;

FIG. 5 is a front elevation view of the chair backrest of the present design;

FIG. 6 is a bottom plan view of the chair backrest of the present design; and,

FIG. 7 is a top plan view of the chair backrest of the present design.

The broken lines and the dashed lines form no part of the claimed design. 

The ornamental design for a chair backrest, as shown and described. 